The present invention relates to an improved thermocouple connection for use with a platinum/rhodium bushing of the type used for the drawing of glass fibers and, more particularly, is directed to such a connection which maintains its calibration throughout the useful life of the bushing.
In the prior art, thermocouples are commonly used to monitor the temperature of bushings used for the drawing of glass fiber. These bushings are coupled to controllers which, in turn, are coupled to power transformers for supplying current to resistance heat the bushings. Ideally, the thermocouple output is used by the controller to maintain constant the temperature of the bushing.
In practice, it has been found that prior art thermocouple control circuits do not, in fact, maintain bushing temperature constant. Rather, as the bushing ages, the circuits gradually increase bushing temperature. This, in turn, has the undesirable effect of changing the physical character (e.g. fiber thickness) of the glass fiber being drawn. It also effects bushing through-put.
Although it is possible to recalibrate the thermocouples of the prior art to correct the above-mentioned problem, this proves very difficult as a practical matter because of the gradual and continuous nature of the change of thermocouple output.